Select query for a login

Question

I'm trying to make a login form, but select query isn't working. Is there another syntax in WordPress and in which way is password hashed? My code is:

if ( isset( $_POST['submit'] ) ) {
    if ( !$_POST['username']  ) {
        echo "You did not complete all of the required fields";
    } else { 
        $username=$_POST['username'];
        $password=$_POST['password'];
        $query = $wpdb->get_row( "SELECT * FROM $wpdb->wp_users
            WHERE user_login='@admin' && user_pass = 'some_pass'" );
        if ( $query != null ) {
            echo "Login success";
            return true;
        } else {
            echo "incorrect pass or user";
            return false;
        }
    }
} 
?>
<form action="" method="post"/>
    <input type="text" name="username" placeholder="Username"/> 
    <input type="text" name="password" placeholder="Password"/><br> 
    <input type="submit" name="submit" value="Submit">
</form>

Answer 1

You can use wp_signon function

Here is an example

    $creds = array();
    $creds['user_login'] = 'example';
    $creds['user_password'] = 'plaintextpw';
    $creds['remember'] = true;
    $user = wp_signon( $creds, false );
    if ( is_wp_error($user) )
        echo $user->get_error_message();

Answer 2

you need to just put it in to variable and that variable call in to query.

  $table_name = $wpdb->prefix . "sign_up";
        $query = $wpdb->get_row( "SELECT * FROM $table_name
            WHERE email_id='".$username."' && password = '".$password."'" );